SAS Protocol Over Ethernet Fabric for Long-Distance SAN Links
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Solution Overview
Problem
The Serial Attached SCSI (SAS) physical layer has a distance limitation of approximately 6 meters, making it unsuitable for communication between host systems and storage controllers in storage area networks (SANs), as it requires a separate physical layer for device-level interconnects.
Innovation Solution
Implementing the SAS storage protocol over an Ethernet fabric, which uses its own physical layer, allowing connections beyond 6 meters without the need for a SAS physical layer, and providing congestion management and priority of service functions through Ethernet protocols or enhanced Ethernet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SAS physical layer is used for host system to storage controller communication, then device-level interconnect functionality is achieved, but communication distance is limited to approximately 6 meters
Solution Approach 1:
The patent introduces Ethernet as an intermediary physical layer between host systems and storage controllers. Instead of directly connecting SAS devices with limited-range physical layer, the invention uses Ethernet switches and Ethernet physical layer infrastructure to bridge distant host systems and storage controllers, while SAS protocols operate at higher layers for logical communication.
Solution Approach 2:
The patent segments the communication system into distinct layers: Ethernet physical layer handles long-distance physical transmission, while SAS protocols (link layer, transport layer, application layer) handle storage-specific communication logic. This segmentation allows each layer to optimize for its specific function without being constrained by the other's limitations.
2Length of stationary object
If separate SAS physical layer infrastructure is deployed for long-distance communication, then communication distance limitation is overcome, but device complexity and infrastructure cost increase
Solution Approach 1:
The patent leverages the universality of Ethernet infrastructure, which is already widely deployed for general networking purposes. The same Ethernet switches, cables, and physical layer equipment used for standard network communications are reused for SAS storage communication, eliminating the need for specialized long-distance SAS physical layer infrastructure.
Solution Approach 2:
The patent merges storage area network traffic with standard Ethernet network infrastructure. By combining SAS protocol operations over Ethernet physical layer, the invention consolidates storage and networking functions into a unified infrastructure, reducing overall system complexity and eliminating redundant hardware.
3Length of stationary object
If Ethernet is used as physical layer for SAS protocol, then communication distance is extended beyond 6 meters, but congestion management and priority of service functions are required
Solution Approach 1:
The patent enables Ethernet infrastructure to self-manage congestion and priority through standard Ethernet mechanisms such as quality of service (QoS) features, traffic prioritization, and flow control that are already built into modern Ethernet switches. This eliminates the need for external congestion management systems.
Solution Approach 2:
The patent utilizes Ethernet's built-in feedback mechanisms for congestion management, where Ethernet switches monitor traffic conditions and dynamically adjust priority levels, bandwidth allocation, and flow control based on real-time network conditions, ensuring reliable SAS communication over long distances.
Data Source
AI summary
Disclosed are embodiments of a storage area network (SAN), a network interface card and a method of managing data transfers. These embodiments overcome the distance limitation of the Serial Attached Small Computer System Interface (SAS) physical layer so that SAS storage protocol may be used for communication between host systems and storage controllers. Host systems and storage controls are connected via an Ethernet interface (e.g., a legacy Ethernet or enhanced Ethernet for datacenter (EED) fabric). SAS storage protocol is layered over this Ethernet interface, providing commands and transport protocol for information exchange. Since the Ethernet interface has its own physical layer, the SAS physical layer is unnecessary and, thus, so is the SAS distance limitation. If legacy Ethernet is used, over-provisioning is used to avoid packet drops, or alternatively, TCP/IP is supported in order to recover from packet drops. If EED is used, congestion management as well as priority of service functions are provided by the EED protocols.